The initial biological response to spinal cord injury is initiated by intra- and extracellular chemical signals. We compare Raman spectra of injured spinal cord obtained minutes after injury to those of uninjured spinal cord to obtain chemical information that precedes the biological response. We studied 29 rats including both Injured and Control using Raman spectra of spinal cords in vivo. Principal Component Analysis (PCA) indicates that <99% of the variation of these spectra across both Injured and Control groups is accounted for with 3 components. The first component does not vary significantly representing structural materials. The second and third components reflect the variation in the chemistry of the cerebrospinal fluid. We demonstrate the first noninvasive in vivo measurement of pH in the CSF using only Raman spectra. We hypothesize that the earliest inflammatory response to mild contusive injury reflects the chemistry of inorganic phosphate present at abnormally high concentrations, likely due to physical disruption of the blood-brain barrier in the choroid plexus and/or mitochondrial release of phosphate, reacting with CSF water.
We previously reported a new algorithm “PV[O]H” for continuous, noninvasive, in vivo monitoring of hematocrit changes in blood and have since shown its utility for monitoring in humans during 1) hemodialysis, 2) orthostatic perturbations and 3) during blood loss and fluid replacement in a rat model. We now show that the algorithm is sensitive to changes in hemoglobin oxygen saturation. We document the phenomenology of the effect and explain the effect using new results obtained from humans and rat models. The oxygen sensitivity derives from the differential absorption of autofluorescence originating in the static tissues by oxy and deoxy hemoglobin. Using this approach we show how to perform simultaneous, noninvasive, in vivo, continuous monitoring of hematocrit, vascular volume, hemoglobin oxygen saturation, pulse rate and breathing rate in mammals using a single light source. We suspect that monitoring of changes in this suite of vital signs can be provided with improved time response, sensitivity and precision compared to existing methodologies. Initial results also offer a more detailed glimpse into the systemic oxygen transport in the circulatory system of humans.
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